The present invention relates to a method preventing charge-up in of objects to be irradiated in an apparatus utilizing ion beams and an ion implanting apparatus and, more particularly, to a charge-up prevention method which is effective for preventing wafers from charging in a heavy current ion implanting apparatus.
In this paper, an object to be irradiated is referred to as an irradiating object.
In conventional measurement of a charging quantity on a wafer, a charge up monitor in which a non-contact gauge head is disposed on a side opposite to a measuring object has been used. The charge up monitor is mounted for use on an opposite side of one of a plurality of (usually circularly arranged) wafers which is receiving beams thereon. A quantity of charge on a wafer increases when beams are being impinged, and decreases as the wafer goes away from the beams by rotation of the wafers. Therefore, the quantity of charge at the position at which beams are really impinging cannot be measured, so that there was a problem that a precise amount of electrons for neutralization cannot be supplied by the conventional method. Furthermore, there has been a problem that the conventional measuring method could not be used for an irradiating object or objects to be treated under a high temperature. This is because the charge quantity measuring equipment cannot be generally used under a high temperature condition over a few hundred .degree.C.
One method of forming implanted oxide films in silicon wafers is SIMOX (Separation by Implanted Oxygen) implanting oxygen ions at a high dose level. In implanting equipment realizing this implanting method, high electric-current oxygen ion beams of 50-70 mA at 120-200 keV are implanted while heating a wafer to a temperature of 500.degree. C. or more. Therefore, the wafer is charged by ion beams, and electric breakdown occurs between the wafer and a holder mounting the wafer thereon. Thus, the charge-up phenomena has resulted in a cause of generating particles due to the electric breakdown.